Enhanced susceptibility of channel catfish to the bacterium Edwardsiella ictaluri after parasitism by Ichthyophthirius multifiliis

Bacterium Edwardsiella ictaluri and parasite Ichthyophthirius multifiliis (Ich) are two common pathogens of cultured fish. The objective of this study was to evaluate the susceptibility of channel catfish Ictalurus punctatus to E. ictaluri and determine bacterial loads in different fish organs after parasitism by Ich. Fish received the following treatments: (1) infected by I. multifiliis at 5000 theronts/fish and exposed to E. ictaluri; (2) infected by I. multifiliis alone; (3) exposed to E. ictaluri alone; and (4) non-infected control. E. ictaluri in fish organs were quantified by quantitative real-time polymerase chain reaction and reported as genome equivalents per mg of tissue (GEs/mg). The results demonstrated that the Ich-parasitized catfish showed significantly (P<0.05) higher mortality (91.7%) when exposed to E. ictaluri than non-parasitized fish (10%). The bacterial loads in fish infected by 5000 theronts/fish ranged from 6497 to 163,898 GEs/mg which was between 40 and 2000 fold higher than non-parasitized fish (49-141 GEs/mg). Ich infection enhanced the susceptibility of channel catfish to bacterial invasion and increased fish mortality.     

Effect of penicillin on the humoral and cellular immune response following group A streptococcal pharyngitis.

The effect of oral and parenteral penicillin on the development of cellular and humoral immune responses in chimpanzees infected with group A streptococcal M-types 1, 5 and 12 was investigated. The interrelationship between type-specific antibody response and enhancement of phagocytic competence of polymorphonuclear neutrophils was documented. Penicillin depressed or suppressed type-specific antibody response depending on the mode and dose of administration, probably because of its effect on the streptococci responsible for antibody stimulation. Penicillin was not demonstrated to have a direct effect on phagocytic ability in vitro. Therefore the primary effect of antibiotic therapy is the indirect relationship to suppression or inhibition of type-specific antibody response to M-protein which results in a diminution of phagocytic competence.     

Parasitism by protozoan Ichthyophthirius multifiliis enhanced invasion of Aeromonas hydrophila in tissues of channel catfish

Protozoan Ichthyophthirius multifiliis Fouquet (Ich) and bacterium Aeromonas hydrophila are two common pathogens of cultured fish, which cause high fish mortality. Currently there is no information available for the effect of parasitism by Ich on survival of channel catfish and invasion of A. hydrophila in fish tissues following exposure to A. hydrophila. A trial was conducted in this study to: (1) determine whether A. hydrophila increased fish mortality in Ich-parasitized channel catfish; and (2) compare the bacterial quantity in different tissues between non-parasitized and Ich-parasitized catfish by real-time polymerase chain reaction (qPCR). The results demonstrated that the Ich-parasitized catfish showed significantly (P<0.05) higher mortality (80%) when exposed to A. hydrophila by immersion than non-parasitized fish (22%). Low mortality was observed in catfish exposed to Ich alone (35%) or A. hydrophila alone (22%). A. hydrophila in fish tissues were quantified by qPCR using a pair of gene-specific primers and reported as genome equivalents per mg of tissue (GEs/mg). Skin, gill, kidney, liver and spleen in Ich-parasitized fish showed significantly higher load of A. hydrophila (9400-188,300 GEs/mg) than non-parasitized fish (4700-42,100 GEs/mg) after exposure to A. hydrophila. This study provides evidence that parasite infections enhance bacterial invasion and cause high fish mortality.     

Streptococcus iniae infection and tissue distribution in hybrid striped bass (Morone chrysops×Morone saxatilis) following inoculation of the gills

This study was designed to test the possibility that Streptococcus iniae enters through the gills and causes infection in hybrid striped bass. To determine the dose response, four groups of fish were inoculated with S. iniae via the gills with a dose of 5.0×10⁵, 2.6×10⁶, 5.0×10⁶, or 1.0×10⁸ CFU/fish. One group of fish was inoculated with tryptic soy broth (TSB) via the gills to serve as controls. The cumulative percent mortality was 13%, 27%, 100% and 100% for 5.0×10⁵, 2.6×10⁶, 5.0×10⁶ and 1.0×10⁸ CFU/fish, respectively. We also examined the tissue dissemination of S. iniae at 0.5, 4, 8, 12, 24, 48 and 72 h after experimental gill inoculation. Fish were inoculated with 2.6×10⁶ or 5.0×10⁶ CFU/fish, which caused low and high mortality, respectively. Within 48 h, fish inoculated with the 2.6×10⁶ dose were culture positive on the gill surface, blood of the first and second gill arches, blood of the third and fourth gill arches and the nares. However, for the dose of 5.0×10⁶ CFU/fish, S. iniae was also isolated from the olfactory, optic and cerebellum regions of the brain, eye, head kidney, trunk kidney, spleen and liver at 48 h. For the 2.6×10⁶ dose, S. iniae was not isolated until 48 h post-inoculation, but was isolated at 12 h for the 5.0×10⁶ dose. The results of this study indicate that S. iniae can enter hybrid striped bass through the gills. However, mortality at similar S. iniae doses was lower than we previously observed by inoculation of the nares.     

Effect of short-term feeding duration of diets containing commercial whole-cell yeast or yeast subcomponents on immune function and disease resistance in channel catfish, Ictalurus punctatus

Juvenile channel catfish, Ictalurus punctatus, were fed diets supplemented with yeast or yeast subcomponents (YYS) as commercial preparations of β‐glucan (MacroGard^® and Betagard A^®), mannan oligosaccharide (Bio‐Mos^® Aqua Grade), or whole‐cell Saccharomyces cerevisiae (Levucell SB20^®) at the manufacturers’ recommended levels. Fish were fed experimental diets for 1 or 2 weeks prior to disease challenge (pre‐challenge feeding periods) and sampled at the end of each feeding period to measure haematological and immune parameters and to determine the effects of dietary YYS on resistance to Edwardsiella ictaluri, the causative agent of enteric septicaemia disease (ESC). Feeding of experimental diets continued for 3 weeks post‐challenge. In channel catfish fed diets supplemented with MacroGard^®, Betagard A^®, or Levucell SB20^®, survival in the 1 week pre‐challenge feeding group and antibody titres in the 2 week feeding group were significantly higher post‐E. ictaluri challenge in relation to catfish fed with the control diet. In fish fed these same three diets, survival to ESC was significantly higher after 1 week vs. 2 weeks feeding, while the antibody response was significantly higher after 2 weeks vs. 1 week. Lysozyme activity was also higher in the 1 week feeding group, but the increased activity was unrelated to diet. Feeding YYS‐supplemented diets for a shorter duration of 1 week prior to challenge may prove beneficial in increasing resistance to ESC in channel catfish. However, we cannot discount that feeding YYS diets during the recovery period may have contributed to ‘glucan overload’ and reduced survival in the 2 week feeding group.     

Immune Response and Resistance to Stress and Edwardsiella ictaluri Challenge in Channel Catfish, Ictalurus punctatus, Fed Diets Containing Commercial Whole-Cell Yeast or Yeast Subcomponents

Dietary supplementation of yeast or yeast subcomponents (YYS) as commercial preparations of β‐glucan (MacroGard^®; Biotec‐Mackzymal, Tromsø, Norway; and Betagard A^®; Aqua‐In‐Tech, Inc., Seattle, WA, USA), mannan oligosaccharide (Bio‐Mos? Aqua Grade; Alltech, Nicholasville, KY, USA), or whole‐cell Saccharomyces cerevisiae (Levucell SB20^®; Lallemand Animal Nutrition, Milwaukee, WI, USA) at the manufacturer’s recommended levels was evaluated on the physiological performance of juvenile channel catfish, Ictalurus punctatus. Fish were fed YYS diets for 4 wk, followed by 2 wk of control diet. Fish were sampled at the end of each feeding period (4 and 6 wk) to measure hematological and immune parameters and growth and to determine the effects of dietary β‐glucan on resistance to Edwardsiella ictaluri infection and to low‐water stress (6 wk). Supplementation of YYS in diets did not affect growth performance, hematology, or immune function. Survival from E. ictaluri infection was from 5 to 17.5% higher in fish fed YYS diets than in the control group, but the increases were not significant. Some improvement in stress resistance was observed in YYS‐fed catfish after exposure to low‐water stress. Stress reduction in fish fed diets supplemented with yeast subcomponents has been reported previously, but thus far, no explanation has been proposed for this effect. The present study and the previously published research suggest that dietary YYS supplementation does not appear to improve resistance of channel catfish to E. ictaluri.     

Protective immunity against enteric septicaemia in channel catfish, Ictalurus punctatus (Rafinesque), following controlled exposure to Edwardsiella ictaluri

Protective immunity against enteric septicaemia of catfish (ESC) following immunization with Edwardsiella ictaluri bacterins and exposure to live E . ictaluri was investigated. Mean cumulative percentage survival was significantly higher ( P 0.05) in controlled live vaccinates (100%) than in immersion and oral bacterin vaccinates (68.3% and 50.0%, respectively). Bactericidal activity against E . ictaluri by peritoneal macrophages from controlled live vaccinates (85.9%) was significantly greater ( P 0.05) than bactericidal activity of macrophages from immersion bacterin vaccinates (71.4%) or non-vaccinates (68.1%). No significant ( P > 0.05) difference was found in the bactericidal activity of macrophages from oral bacterin vaccinates and macrophages from controlled live vaccinates. The E . ictaluri -specific antibody response of controlled live (0.08 OD) and immersion bacterin vaccinates (0.11 OD) was significantly higher ( P 0.05) than that of oral bacterin vaccinates and non-vaccinates (0.01 OD) 15 days post-vaccination. A significantly higher antibody response was seen in controlled live vaccinates (0.17 OD), when compared to other vaccinates or non-vaccinates 33 days after vaccination. Neither immersion nor oral bacterins protected the vaccinates against ESC. Controlled live E . ictaluri immunization of channel catfish resulted in production of specific antibodies, increased macrophage bactericidal activity and protection against ESC.     

Lymphocyte stimulation in swine dysentery

In lymphocyte stimulation studies of pigs affected with swine dysentery (SD) all of the pigs gave significant response (P < 0.05) to soluble antigen from $\text{Treponema}$$\text{hyodysenteriae}$. Swine infected with virulent or attenuated $\text{T.}$$\text{hyodysenteriae}$ gave significant lymphocytic response 3 or 6 weeks after infection; uninfected pigs did not give a similar lymphocytic response. The delayed hypersensitivity (DH) skin test, in which soluble $\text{T.}$$\text{hyodysenteriae}$ antigen preparation was used, detected only 3 out of 14 SD-affected swine. The lymphocyte stimulation assay by detection of protein synthesis may offer a rapid, reliable test for the diagnosis of SD within herds suspected of being affected.     

Determination of macrophage chemotaxis to atherosclerotic plaque extract in domestic turkeys with hypertension

The chemotactic activity of turkey peritoneal macrophages in response to an atherosclerotic plaque extract from a hypertensive strain of turkeys was determined. Atherosclerotic plaque extract stimulated macrophage chemotaxis, whereas normal aortic extract did not stimulate macrophage chemotaxis. However, differences were not revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of extracts of atherosclerotic plaque and normal aorta. Chemotactic activity was diminished with pronase treatment, suggesting the chemo-attractant is a protein. Seemingly, atherosclerotic plaque of turkeys contains a macrophage chemotaxin.